This application claims the priorities of Korean Patent Application No. 2002-26023, Korean Patent Application No. 2002-28919, and Korean Patent Application No. 2003-3466, respectively filed on May 11, 2002, May 24, 2002, and January 18, 2003, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference.
1. Field of the Invention
The present invention relates to a surface light source apparatus, and more particularly, to a surface light source apparatus for forming a light guide pattern portion by scanning a laser beam using a head moving portion capable of moving above a light guide panel in vertical and horizontal directions, a method of manufacturing the surface light source apparatus, and an apparatus for manufacturing the surface light source apparatus.
2. Description of the Related Art
In general, a light guide panel is a plate providing a path through which light scanned from a light source is uniformly scattered and diffused. The light guide panel is applied to a light receiving flat display panel such as an LCD device, or a surface light source apparatus used for an illuminating signboard.
As a surface light source apparatus, a method of arranging a cold cathode fluorescent lamp (CCFL) or an LED, and a flat panel fluorescent lamp method in which a circuit board coated with a fluorescent material is assembled, are widely used. The CCFL can be classified into an edge light type using a light guide panel and a direct light type in which the light sources are arranged on a flat surface to overlap one another, according to the arrangement of a light source with respect to a display surface. These surface light source apparatuses are disclosed in Korean Patent Application Nos. 93-11174, 94-26117, 94-33115, 94-26116, and 2000-44725.
Referring to FIG. 1, a conventional surface light source apparatus 10 includes a light guide panel 11, a reflection panel 12 installed under the light guide panel 11, a light source 13 installed on a side wall of the light guide panel 11, and a cover member 14 covering the light source 13. A CCFL or an LED can be used as the light source 13.
A plurality of light guide pattern portions 15 printed using titanium oxide TiO2 having a bead shape and ink including glass or acryl to scatter and diffuse light incident on one surface of a transparent acryl resin is formed on the light guide panel 11.
In the surface light source apparatus 10 having the above structure, light emitted from the light source 13 is incident on the light guide panel 11. The incident light is guided through the light guide panel 11 as indicated by an arrow and reflected by the reflection panel 12 and the light guide pattern portions 15 to have a relatively uniform intensity of illumination at each portion thereof.
However, the light guide pattern portions 15 formed in a print method has the following problems.
The processes of manufacturing and printing of ink to form the light guide pattern portions 15 are very complicated, and part of printed portions can be removed or smeared is high so that a defective ratio is very high. Yield of the light guide pattern portions 15 is about 80 through 90%, which is relatively low. Also, since the light guide panel 11 on which the light guide pattern portions 15 are not printed well cannot be reused after the light guide pattern portions 15 are removed, a manufacturing cost is increased.
In particular, since the light guide pattern portions 15 utilize optical reflection of a printed ink object itself, the ink object unavoidably absorbs light. The light absorption phenomenon lowers an efficiency of light of the surface light source apparatus.
Also, as shown in FIG. 2, a surface S of the light guide panel 11 is typically regularized to have a very small thickness deviation t1 of about ±100 μm. Accordingly, a cost of a raw material of a product is relatively high. If the thickness deviation is regularized relatively greater, the cost of a raw material of a product can be lowered. However, when a screen 21 having a predetermined pattern containing ink objects is arranged on the surface S of the light guide panel 11 and the ink objects are printed by using a squeegee 22, the amount of coated ink in each area of the light guide panel 11 differs from one another by more than 50% due to the thickness deviation t1 and the size of each of the light guide pattern portions 15 changes to 50 through 100 μm.
To solve the above problem, conventionally, a non-print method is adopted as shown in FIG. 3. As the non-print method, there is a stamping method using a mold and an injection mold method.
Referring to FIG. 3, a surface light source apparatus 30 includes a light guide panel 31, a reflection panel 32 installed under the light guide panel 31, and a light source 33 installed at a side wall of the light guide panel 31. A plurality of light guide pattern portions 34 having a plurality of grooves having conic shapes are formed on the light guide panel 31 by heating and pressing the light guide panel 31 using a mold having a protruding portion on one surface thereof. The shape of the section of the light guide pattern portion 34 forms a V shape, as shown in FIG. 4.
In the surface light source apparatus 30 having the above structure, light emitted from the light source 33 is incident on the light guide panel 31. When the incident light proceeds in the light guide panel 31, part of the light is reflected by an inclined surface of the light guide pattern portion 34.
However, the light guide pattern portion 34 has the following problem.
Since the light guide pattern portion 34 is formed in a heat and press method using a mold, the management of the process is very difficult. In particular, since acryl resin which is a material of the light guide panel 31 is very weak at heat, the light guide pattern portion 34 having a desired pattern cannot be accurately made.
Also, the above method realizes a surface light source simply by optical reflection by a mirror, which lowers the diffusiveness of light. As a result, a phenomenon that the shape of the light guide pattern portion 34 appears strongly, occurs. To prevent the phenomenon, a diffusion sheet is additionally arranged, however, the phenomenon is not completely removed.
Further, as shown in FIG. 5, the light guide panel 31 typically has a thickness deviation t2 about ±100 μm. When the light guide pattern portion 34 is processed on the light guide panel 31 using a mold 51 having a processing depth of about 100 μm, a protruding portion 52 formed on the mold 51 can form the conic grooves at the thickest portion of the light guide panel 31 by heating and pressing the portion to the depth of 100 μm. However, at the thinnest portion of the light guide panel 31, the light guide pattern portion 34 is not processed at all.
Thus, to obtain an optimal light guide efficiency, a material having a very precise thickness deviation is needed and more than tens of correction works of the mold 51 should be repeated. Consequently, the cost for development rises. In addition, since the manufacturing duration of the mold 51 is extended, development of a variety of products is made difficult.